Eutectic alloy shaped charge liner



1366- 1963 J. w. GEHRING, JR

EUTECTIC ALLOY SHAPED CHARGE LINER Filed Dec. 11, 1959 FIG.'?-

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United States Patent 3,112,709 EUTECTIC ALLOY SHAPED CHARGE LINER John W. Gehring, in, 8300 Alston Road, Towson 4, Md. Filed Dec. 11, 1959, Ser. No. 859,674 5 Claims. (Cl. 102--20) (Granted under Title 35, US. Code (1952), see. 266) The invention described herein may be manufactured and used by or for the Government for governmental purposes without the payment to me of any royalty thereon.

This invention relates to improvements in materials for use in fabricating liners for shaped charges.

Heretofore, a single metal has been used as a liner for shaped charges, but it has been found that an alloy employed as a liner has distinct advantages over the pure metal liner provided that constituents of the alloy are so chosen or selected that desired physical properties of certain metals are combined in such a manner as to produce the desired result.

Shaped charges may be of various sizes and dimensions, but generally they are conical in shape and Where the word cone is used, the conical charge is referred to, the base or mouth of the cone facing the object to be penetrated.

The principal object of this invention is the employment of a liner for a shaped charge to improve the pene-- tration capability of the charge and to obtain a clean, slug-free hole in the target.

It is a further object of this invention to utilize this improved liner for a shaped charge in the piercing'of armor plate or more particularly in the perforating of an oil well casing.

The discovery that direction could be given to the destructive effect of an explosive charge by providing a shaped cavity in the wall of the charge led to the employment of such charges against armor plate and sub- P=L Pt Where P represents the penetration, L represents the length of the jet (before it begins to break up), P represents the density of the metal comprising the jet, and P represents the density of thetarget metal' The target metal in all practical cases will be steel, and therefore P, will remain essentially constant. The density of the jet metal may be varied by employing liners of dilferent metals. It will be observed that, according to the formula, the penetration varies directly as the square root of P,-. The penetration also varies direct-1y with L, the length of the jet.

A closer examination of the quantity L is necessary for better understanding of this invention. It should be understood that upon detonation the liner of a shaped charge undergoes deformation, or working at an enormous pressure which is far beyond the pressure ranges that are obtained under any other known process of metal Working. It appears that the jet formation is an exremely rapid and violent extrusion of the metal, and therefore it is logical to assume that the ductility of the metal comprising the jet is a most important factor "ice in avoiding an early break-up of the jet and thus realizing a continuous jet of great length. In search for an ideal material to obtain this result, one must be se-.

lected that has the property of infinite ductility.

The means for obtaining maximum penetration, therefore, based upon the previous discussion, appears to be the selection of the densest, most ductile material, would result in the greatest penetration. Investigation has shown, however, that there are factors involved which are not fully understoodv and are not expressed by the basic formula.

It is now supposed that under conditions of high rate strain deformation of metals such as occurs in the shaped charge jet, the behavior of a particular metal does not follow the course one would predict from the ductility observed under normal conditions. The problem is one of predicting the ductility of metals under high strain rate deformation (3300,000 p.s.i. or higher). It has been observed that uniform fine grain eutectic compositions exhibit penetration characteristics markedly superior to the pure metals from which the alloy is made, or to other alloy proportions. served that, of the eutectic compositions, those in which a brittle phase is uniformly dispersed throughout a ductile matrix are superior in penetration characteristics to eutectic compositions in general. In order to insure a ductile matrix on a practical scale, it has been found necessary to shade the alloy composition toward the more ductile constituent so that the structure observed will include incipient dendrites of the ductile constituent. The dendrites are termed incipient to emphasize the fact that the dendritic structure obtained is discontinuous, for, as the dendritic structure becomes more pronounced, to the point where continuous masses of the ductile constituent assume this structure, the penetration of the liners from such material drops off sharply. A liner material which Will yield reproducible optimum penetration data, and which lends itself to manufacture on a large scale, may be particularly described as an essentially eutectic composition having a fine grain structure in which a brittle phase is uniformly dispersed in a ductile matrix with the amount of the ductile constituent being sufficiently in excess of the eutectic proportion to induce the formation of discontinuous dendrites of the ductile constituent.

A slug-free hole in the target can be obtained by using one of the low-melting point pure metals; lead, tin, cadmium, or zinc. A slug-free hole plus the marked improvement in penetration can only be obtained by the use of a low-melting point alloy having specific mechanical and structural properties best obtained with eutectic alloys of either lead-antimony, cadmium-antimony, or cadmium-nickel. The final structure of the alloy, whether it be cast or drawn in the forming process, must be such that the soft ductile constituent (i.e. lead) forms the continuous matrix while the hard, less ductile constituent (i.e. antimony) forms a uniformly dispersed non-continuous brittle phase. When this structure is realized while using only the eutectic composition of the particular alloy system, it is possible to obtain 10-11 calibres of penetration into mild steel, and further 7 to obtain a slug-free hole in the target.

From the Metals Handbook published by American Society for Metals, 1948 ed., the eutectic composition of suitable alloys are as follows:

88.8% Pb-ll.2% Sb 92.5% Cd-7.5% Sb 99.7% Cd.25% -Ni 61.9% SI138.1% Pb 82.5% Pb-17.5% Cd 71.9% Ag28.1% Cu Patented Dec. 3., 1963 Further, it has been ob- The uniformity of the eutectic matrix is important in obtaining maximum penetration. The preparation of each alloy is dependent upon the particular susceptibilities of each alloy toward variations in the techniques of melting, pouring, risering, gating, and moulding practice. In addition to these variables, the resultant microstructure of the cast alloy is dependent upon the mold temperature, the melt temperature, and the rate of cooling of the melt to the point of solidification. The a1- loys used were cast in permanent steel molds whose temperature was varied between 380 and 460 Fahrenheit While the metal temperature was varied between 63*) and 849 Fahrenheit.

in the drawings, FEGURES 1 to 8 inclusive illustrate the typical microstructure of both cast lead and lead-antimony eutectic alloy liners and their corresponding depth of penetration into mild steel for different methods of casting.

It can be observed that FIGURES l, 4 and 6 are of similar type and yield the best penetrations. These structures can be properly defined as a discontinuous dendritic growth, wherein the black areas represent primary lead dispersed in the eutectic matrix.

FKGURES 2 and 3 exhibit concentrations of lead in a better defined dendritic growth which are non-uniformly dispersed throughout the cone.

FIGURE 5 contained an excess of antimony in the melt which appears in the final cast micro-structure as the well defined white crystals.

The structures shown in FIGURES 2, 3 and 5 yield the poorest mean penetrations and also have the largest standard deviations at each standoff. The non-uniform structures appear to cause an erratic transmission of the shock wave through the material, resulting in an asymmetric collapse of the liner. A similar dependency of penetration on the microstructure of the cone shown in FIG- URES 7 and 8, wherein lead-antimony eutectic liners having two different microstructures were tested. The results indicate that structures similar to those in FIGURE 7 do not perform as well as those similar to the structure shown in FIGURE 8.

The desirable microstructure is defined as a uniformly dispersed brittle phase of fine dendritic growth, in a ductile matrix and is shown in FTGURES l, 4 and 6 which are of extremely fine dispersion of the eutectic matrix containing areas of primary lead. These areas of primary lead are in themselves non-uniformly dispersed, while in FIGURES 2 and 3, the areas of primary lead appear in a dendritic growth pattern having both primary and secondary arms. This latter type of dendritic growth is detrimental to the uniform collapse process of the alloy liner. These non-uniformities were best illustrated by experiment wherein a typical lead-antimony alloy liner and typical pure lead liner were loaded internally with pentolite explosive and detonated from the base end of the cone. In this manner the high pressure gases formed upon detonation of the explosive caused the cone to expand in outward direction in reverse of the process occurring during collapse of a shaped charge liner. This reversal of the process was necesary in order to simultaneously load the material at the same rate and the same pressures and temperature and still be able to view the expansion or deformation of the wall. The results indicate that the pure lead liner, which is homogeneous in microstructure, expanded very uniformly with no off-shoots or jets appearing on the surface; the lead-antimony cone developed little jets spurting out on the surface in the expansion process, thus indicating that these areas are areas which yielded more readily than did their adjacent areas. Thus this ex eriment demonstrates that the expansion process clearly demonstrates that non-uniformities in the structure of the cone will lead to non-uniformities in the collapse process, and the material of the cone will not collapse in a symmetric fashion and yield a good jet. Con- A versely, the eutectic mttrix must be of uniformly finely ground composition, which upon detonation of the charge produces a symmetrical collapse of the alloy liner thereby obtaining greater penetration of the target, and complete dispersion of the slug within the walls of the hole.

It has been found desirable to also increase the thickness of the liner when utilizing the alloys heretofore described, to obtain even greater penetration of the target and a larger slug-free hole.

This invention is designed particularly to improve the piercing of armor-plate and the perforation of oil-well casings. Particularly the latter, as the larger, longer, cleaner, slug-free hole is of great assistance in the perforating of the oil-bearing formation without the casing. The hole so produced lends itself to repeated explosive charges without incurring the loss of time necessary to remove the ordinary slug.

It is obvious that this invention has many other applications and should only be limited by the hereinafter appended claims.

1 claim:

1. A liner for a shaped charge consisting of an alloy having a eutectic composition comprising a fine grain relatively brittle phase of antimony uniformly dispersed in a ductile matrix of fine grain lead and non-uniformly distributed discontinuous dendrites of primary lead.

2. The method of perforating an oil well casing comprising, utilizing a shaped charge, lining the shaped charge with an alloy of eutectic composition having a fine grain structure in which a brittle phase of antimony is uniformly dispersed in a ductile matrix of lead with the amount of lead sufiiciently in excess of the eutectic proportion to induce the formation of non-uniformly distributed discontinuous dendrites of lead, positioning within the walls of the Well the casing containing the charge, detonating the charge to perforate the casing and produce a hole in the wall of the well, vaporizing the ductile lead of the liner by the heat generated by the charge to fuse said lead dendrites with the walls of the hole to produce a slug free penetration.

3. A metal liner for a shaped charge comprising an alloy of essentially eutectic composition having a fine grain relatively brittle phase of a metal selected from a group consisting of antimony and nickel uniformly dispersed in a ductile matrix of a fine grain metal selected from a group consisting of lead, tin, antimony and zinc, the amount of the ductile constituent being suificiently in excess of the eutectic composition to induce the formation of non-uniformly distributed discontinuous dendrites of the primary form of the ductile constituent within the matrix.

4. A method of perforating an oil well casing comprising, utilizing a shaped charge, lining the shaped charge with an alloy of eutectic composition having a fine grain structure in which a brittle phase of a metal selected from the group consisting of antimony and nickel is uniformly dispensed in a ductile matrix of a fine grain metal selected from the group consisting of lead, cadmium, tin and zinc with the amount of the ductile constituent being sufficiently in excess of the eutectic proportion to induce the formation of non-uniformly distributed discontinuous dendrites of the ductile constituent, positioning within the walls of the well the casing containing the charge, detonating the charge to perforate the casing and produce a hole in the wall of the well, vaporizing the ductile constituent of the liner by the heat generated by the charge to fuse said ductile dendrites Within the Walls of the hole to produce a slug free penetration.

5. A liner for a shaped charge consisting of an alloy having an eutectic composition comprising a fine grain relatively brittle phase of nickel uniformly dispersed in a ductile matrix of fine grain cadmium and non-uniformly distributed discontinuous dendrites of primary cadmium.

(References on following page 5 References Cited in the file of this patent UNITED STATES PATENTS Lawson Aug. 5, 1952 Church et a1; Feb. 2, 1954 5 tute of Mining and Metallurgical Engineers, written by George B. Clark (page 7 relied on).

Technical Publication No. 2158 of the American Insti- I tute of Mining and Metallurgical Engineers, written by George B. Clark (only first page relied on).

Metals Handbook, 1948 edition, published by American Society for Metals (page 750). 

3. A METAL LINER FOR A SHAPED CHARGE COMPRISING AN ALLOY OF ESSENTIALLY EUTECTIC COMPOSITION HAVING A FINE GRAIN RELATIVELY BRITTLE PHASE OF A METAL SELECTED FROM A GROUP CONSISTING OF ANTIMONY AND NICKEL UNIFORMLY DISPERSED IN A DUCTILE MATRIX OF A FINE GRAIN METAL SELECTED FROM A GROUP CONSISTING OF LEAD, TIN, ANTIMONY AND ZINC, THE AMOUNT OF THE DUCTILE CONSTITUENT BEING SUFFICIENTLY IN EXCESS OF THE EUTECTIC COMPOSITION TO INDUCE THE FORMATION OF NON-UNIFORMLY DISTRIBUTED CISCONTINUOUS DENDRITES OF THE PRIMARY FORM OF THE DUCTILE CONSTITUENT WITHIN THE MATRIX. 